Add hierarchy_delimiter to IMAP account, set it when claiming a session.
Add hierarchy_delimiter to IMAP account, set it when claiming a session.

* src/engine/imap/api/imap-account.vala (Geary.Imap.Account): Add
  hierarchy_delimiter.
  (claim_session_async): Always do an (X)LIST so hierarchy_delimiter gets set.
  (list_inbox): Renamed from determine_xlist_inbox, do a LIST or XLIST as
  appropriate, set the account's INBOX's specifier and
  hierarchy_delimiter from the result.

tshikaboom/geary,mjog/geary,mjog/geary,mjog/geary,tshikaboom/geary,robol/geary,robol/geary,tshikaboom/geary,robol/geary